Recently, the development of the backbone network communication line as mainly focusing on the optical fiber communication technology is proceeding steadily, in such a situation, the electronic wirings in the information terminal are becoming a bottleneck. Against such background, instead of the conventional electric circuit substrate in which all signal transmissions are made by using the electric signal, the optoelectronic composite substrate (the optical waveguide device) of the type that transmits high-speed parts by the light has been proposed, in order to compensate the limit of transmission speed of the electric signal.
In the optoelectronic composite substrate, the light signal is transmitted by the optical waveguide including such a structure in which the core layer is surrounded by the cladding layers.
In Patent Literature 1 (Japanese Laid-Open Patent Publication No.2006-119216), it is set forth that the lower cladding layer, the core layer, and the upper cladding layer are formed sequentially on the substrate, then the first and second groove portions which divide the core layer from the upper cladding layer side are formed, and then the first and second mirrors are formed by providing the metal film on the first and second groove portions.
As explained in the related art described later, in the method of forming the light path conversion mirror which is optically coupled to the optical waveguide, first, the groove portion which includes the light path conversion inclined surface arranged on the outer side and the sidewall surface (the perpendicular surface) which intersects with the light path conversion inclined surface is formed on both end sides of the optical waveguide respectively. Then, the metal layer is formed selectively on the inner surfaces of the groove portions, and then the unnecessary metal layer formed on the sidewall surfaces is removed, whereby the light path conversion mirror formed of the metal layer is obtained on the light path conversion inclined surface.
However, the micro fabrication is necessary in order to remove the metal layer on the sidewall surfaces of the groove portions. Therefore, there is necessity to specially employ the laser beam machining using an excimer laser or the high-performance photolithography. As a result, such a problem arises that an increase in cost is brought about.
Also, there is the method of removing the metal layer by cutting the metal layer on the sidewall surface of the groove portion by means of the cutting device. In this event, such a problem arises that either the cutting shavings adhere to the metal layer (the light path conversion mirror) of the light path conversion inclined surface, or the metal layer peels off or deforms.